Sheet feeding apparatus with mechanism for detecting sheet feeding state and sheet feeding method

Abstract

A sheet feeding apparatus includes first and second sheet sensors provided in order from upstream to downstream sides in feeding direction on a paper feed path, sheet conveyor roller sets arranged along the path, and a roller controller individually controlling groups of rollers on the upstream and downstream sides of the first sheet sensor, in response to a change in values of output signals from first and second sheet sensors. The roller controller includes an overlapped feeding determining device outputting a determination signal assuming a first value when overlapped feeding occurs and a second value otherwise, in response to the change in values of the output signals from the sensors, an overlapped feeding eliminating device eliminating overlapped feeding by controlling the roller controller upon receiving the determination signal of the first value, and a conveyor roller stopping device stopping the sheet conveyor rollers if the overlapped feeding eliminating process should fail.

1. A sheet feeding apparatus, comprising:
 first and second sheet sensors provided in order from upstream to downstream sides in a sheet feeding direction on a paper feed path through which sheets of paper are fed one by one by a prescribed paper feeder, each sensor outputting a signal that is on when a sheet is detected and off otherwise; and 
 a plurality of sets of sheet conveyor rollers arranged at a plurality of positions along said paper feed path; wherein 
 two or more sheets may possibly be fed partially overlapped from said paper feeder to said paper feed path; 
 said plurality of sets of sheet conveyor rollers include a group of upstream rollers on the upstream side than said first sheet sensor, and a group of downstream rollers on the downstream side than said first sheet sensor; 
 said sheet feeding apparatus further comprising: 
 a roller controller connected to receive output signals of said first and second sheet sensors, and individually controlling said group of upstream rollers and said group of downstream rollers in accordance with a change in value of said output signals; wherein 
 said roller controller includes 
 an overlapped feeding determining device activated in response to start of paper feeding from said paper feeder to said paper feed path, and outputting a determination signal assuming a first value when overlapped feeding of sheets has occurred and a second value otherwise, in response to a change in values of output signals of said first and second sheet sensors, 
 an overlapped feeding eliminating device, temporarily stopping driving of said plurality of sets of sheet conveyor rollers until after the lapse of an idle time to effect print registration of sheets before a register roller positioned at a terminal end of said paper feed path, and after a lapse of the idle time, again driving said group of downstream rollers while driving of said group of upstream rollers is kept stopped, by controlling said roller controller, in response to reception of said determination signal of said first value, and 
 a conveyor roller stopping device stopping said group of downstream rollers in response to failure of overlapped feeding elimination by said overlapped feeding eliminating device; wherein 
 said overlapped feeding determining device includes an overlapped feeding occurrence determining device outputting said determination of signal of said first value, when a prescribed time period passed with the output signal from said first sheet sensor kept on, after the output signals from said first and second sheet sensors changed from off to on in this order. 
 
     
     
       2. The sheet feeding apparatus according to  claim 1 , wherein
 said overlapped feeding eliminating device includes 
 an upstream roller stopping device stopping said paper feeder and said upstream rollers, in response to reception of said determination signal of said first value, and 
 a roller activating device activating said paper feeder and said upstream rollers, in response to a change from on to off of the signal output by said first sheet sensor within a prescribed time period from turning on of said second sheet sensor. 
 
     
     
       3. The sheet feeding apparatus according to  claim 2 , wherein
 said conveyor roller stopping device includes a downstream roller group stopping device stopping said group of downstream rollers when said prescribed time period passed with the signal output from said first sheet sensor kept on, after said upstream rollers were stopped by said upstream roller stopping device. 
 
     
     
       4. The sheet feeding apparatus according to  claim 3 , wherein
 said roller controller further includes a conveyor roller reactivating device activating both said upstream and downstream rollers for feeding a sheet from said prescribed paper feeder to said paper feed path, in response to turning off of both output signals from said first and second sheet sensors after said downstream roller group was stopped by said downstream roller group stopping device. 
 
     
     
       5. The sheet feeding apparatus according to  claim 3 , wherein
 said overlapped feeding occurrence determining device includes 
 a timer activated in response to a change from off to on of the output signal of said first sheet sensor, and 
 a circuit outputting said determination signal that assumes a first value if the output signal of said first sheet sensor is on and a second value if it is off, when a prescribed time is counted by said timer, after the output signal of said second sheet sensor is changed from off to on. 
 
     
     
       6. The sheet feeding apparatus according to  claim 3 , wherein
 said downstream roller group stopping device includes 
 a timer activated when said second sheet sensor is turned on, and 
 a device inspecting an output of said first sheet sensor when a prescribed time is counted by said timer and stopping, if the output is on, said downstream roller group. 
 
     
     
       7. The sheet feeding apparatus according to  claim 2 , wherein
 said overlapped feeding occurrence determining device includes 
 a timer activated in response to a change from off to on of the output signal of said first sheet sensor, and 
 a circuit outputting said determination signal that assumes a first value if the output signal of said first sheet sensor is on and a second value if it is off, when a prescribed time is counted by said timer, after the output signal of said second sheet sensor is changed from off to on. 
 
     
     
       8. The sheet feeding apparatus according to  claim 2 , wherein
 said roller activating device includes 
 a timer activated when said second sheet sensor is turned on, and 
 a device inspecting an output of said first sheet sensor when a prescribed time is counted by said timer and activating, if the output is off, said paper feeder and said upstream rollers. 
 
     
     
       9. The image forming apparatus according to  claim 8 , further comprising
 a discharge device discharging, when two or more sheets are fed in partially overlapped manner to said paper feed path and a preceding sheet is for printing last page of said image data, a sheet following the preceding sheet without performing printing process. 
 
     
     
       10. The sheet feeding apparatus according to  claim 1 , wherein
 said overlapped feeding occurrence determining device includes 
 a timer activated in response to a change from off to on of the output signal of said first sheet sensor, and 
 a circuit outputting said determination signal that assumes a first value if the output signal of said first sheet sensor is on and a second value if it is off, when a prescribed time is counted by said timer, after the output signal of said second sheet sensor is changed from off to on. 
 
     
     
       11. The sheet feeding apparatus according to  claim 1 , comprising
 only a pair of said conveyor rollers between said first and second sheet sensors. 
 
     
     
       12. An image forming apparatus, comprising:
 a sheet feeding apparatus feeding sheets of paper on a paper feed path on which sheets of paper are fed one by one by a prescribed paper feeder; and an image forming unit printing image data on the sheet fed through said paper feed path; wherein 
 said sheet feeding apparatus includes 
 first and second sheet sensors provided in order from upstream to downstream sides in a sheet feeding direction on said paper feed path, each sensor outputting a signal that is on when a sheet is detected and off otherwise, and 
 a plurality of sets of sheet conveyor rollers arranged at a plurality of positions along said paper feed path; wherein 
 two or more sheets may possibly be fed partially overlapped from said paper feeder to said paper feed path; 
 said plurality of sets of sheet conveyor rollers include a group of upstream rollers on the upstream side than said first sheet sensor, and a group of downstream rollers on the downstream side than said first sheet sensor; 
 said sheet feeding apparatus further comprising: 
 a roller controller connected to receive output signals of said first and second sheet sensors, and individually controlling said group of upstream rollers and said group of downstream rollers in accordance with a change in value of said output signals; wherein 
 said roller controller includes 
 an overlapped feeding determining device activated in response to start of paper feeding from said paper feeder to said paper feed path, and outputting a determination signal assuming a first value when overlapped feeding of sheets has occurred and a second value otherwise, in response to a change in values of output signals of said first and second sheet sensors, 
 an overlapped feeding eliminating device, temporarily stopping driving of said plurality of sets of sheet conveyor rollers until after the lapse of an idle time to effect print registration of sheets before a register roller positioned at a terminal end of said paper feed path, and after a lapse of the idle time, again driving said group of downstream rollers while driving of said group of upstream rollers is kept stopped, by controlling said roller controller, in response to reception of said determination signal of said first value, and 
 a conveyor roller stopping device stopping said group of downstream rollers in response to failure of overlapped feeding elimination the process for eliminating overlapped feeding by said overlapped feeding eliminating device; wherein 
 said overlapped feeding determining device includes an overlapped feeding occurrence determining device outputting said determination of signal of said first value, when a prescribed time period passed with the output signal from said first sheet sensor kept on, after the output signals from said first and second sheet sensors changed from off to on in this order. 
 
     
     
       13. A method of sheet feeding, in a sheet feeding apparatus including first and second sheet sensors provided in order from upstream to downstream sides in a sheet feeding direction on a paper feed path through which sheets of paper are fed one by one by a prescribed paper feeder, each sensor outputting a signal that is on when a sheet is detected and off otherwise, and
 a plurality of sets of sheet conveyor rollers arranged at a plurality of positions along said paper feed path; wherein 
 two or more sheets may possibly be fed partially overlapped from said paper feeder to said paper feed path; 
 said plurality of sets of sheet conveyor rollers include a group of upstream rollers on the upstream side than said first sheet sensor, and a group of downstream rollers on the downstream side than said first sheet sensor; and 
 said sheet feeding apparatus further includes 
 a roller controller connected to receive output signals of said first and second sheet sensors, and individually controlling said group of upstream rollers and said group of downstream rollers in accordance with a change in value of said output signals; 
 said sheet feeding method comprising: 
 the step, started in response to start of paper feeding from said paper feeder to said paper feed path, of outputting a determination signal assuming a first value when overlapped feeding of sheets has occurred and a second value otherwise, in response to a change in values of output signals of said first and second sheet sensors; 
 the step of temporarily stopping driving of said plurality of sets of sheet conveyer rollers until after a lapse of an idle time to effect print registration of sheets before a register roller positioned at a terminal end of said paper feed path, and after the lapse of the idle time, again driving said group of downstream rollers while driving of said group of upstream rollers is kept stopped, by controlling said roller controller, in response to reception of said determination signal of said first value; and 
 the step of stopping said group of downstream rollers in response to failure of overlapped feeding elimination at said step of driving; wherein 
 said step of outputting includes the step of outputting said determination signal of said first value, when a prescribed time period passed with the input signal from said first sheet sensor kept on, after the output signals from said first and second sheet sensors changed from off to on in this order.